as has been mentioned idle and kickdown are most certainly two different isues.
As have been mentioned already have someone sit in the car,engine shut of,with pedal to the floor check how much more you can push the kickdownlinkagerod back from that possition.
I dont have a clue how your linkage looks or is supposed to look but dont ever belive its right just because its supposed to be right,probably dont need to be correct either to work right.
is there no adjustment of kickdown down at the kickdown lever on the transmission?
Regarding idle,i would look for a vacumleak or timingisue.
Dont know what is a correct idle but i cant see why a stock 340 cant idle at 7-800 or so rpm warm.
Did a check. Flooring the throttle definitely pushes the kickdown rod back as far as it can go and NO kickdown.
